The project is designed to increase our knowledge of the excitation-contraction coupling process in the mammalian heart. The focus is to define the characteristics of calcium (Ca) at the myocardial sarcolemma, including definition of binding sites, factors important in the determination of the quantity bound, relation of bound Ca to transsarcolemmal movement and subsequent cellular distribution and the relation of this Ca to the process of contractile control. Methodology will include (1) zeta potential measurement in vesicles and single cells, (2) vesicle aggregation studies, (3) 45Ca exchange measurement in single cells with "scintillation sieve" technique, (4) measurement of contraction amplitude of single cells by video technique under conditions of rapid perfusion, (5) ionic current measurement with single cell voltage clamp, (6) ionic compartmentation analysis with electron microprobe, (7) membrane ultrastructure with electron microscopy and freeze-fracture technique and (8) measurement of excitation-dependent Ca uptake and function in intact, arterially-perfused ventricular tissue. The project is designed to be comprehensive in that Ca binding characteristics at the molecular level will be correlated with cellular exchange and contractile function. Knowledge gained from this project can be related to contractile control of the heart in situ, as a foundation for comparison of ionic events following cardiac ischemia and reperfusion and to increase understanding of the action of drugs on cardiac function in the clinical situation.